U.S. patent application number 16/023436 was filed with the patent office on 2019-01-03 for method of preparing calcification-resistant bioprosthetic tissue.
This patent application is currently assigned to St. Jude Medical, Cardiology Division, Inc.. The applicant listed for this patent is St. Jude Medical, Cardiology Division, Inc.. Invention is credited to Katherine A. Ahmann, Paul E. Ashworth, Chad Joshua Green, David A. Panus, Jay Reimer.
Application Number | 20190001023 16/023436 |
Document ID | / |
Family ID | 63013098 |
Filed Date | 2019-01-03 |
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United States Patent
Application |
20190001023 |
Kind Code |
A1 |
Ashworth; Paul E. ; et
al. |
January 3, 2019 |
Method Of Preparing Calcification-Resistant Bioprosthetic
Tissue
Abstract
Methods of preparing calcification-resistant bioprosthetic
tissue include providing fresh biological tissue, cross-linking the
tissue, treating the cross-linked tissue with an alcohol for a time
sufficient to allow the alcohol to be diffused into the tissue, and
treating the alcohol-treated fixed tissue with a polyol for a time
sufficient to allow fluid in the tissue to be replaced by the
polyol. The methods may include sterilizing the cross-linked tissue
in a solution including propylene oxide or peracetic acid either
before or after the alcohol treatment step; or drying the
alcohol/polyol-treated, cross-linked tissue, sterilizing the dried
tissue by exposure to ethylene oxide or peracetic acid, and storing
the sterilized tissue in a dry, ambient environment. The treated
tissue may be a tissue component for a bioprosthetic valve, a valve
assembly for a bioprosthetic valve or a fully assembled
bioprosthetic valve incorporating the tissue.
Inventors: |
Ashworth; Paul E.; (Wyoming,
MN) ; Green; Chad Joshua; (Forest Lake, MN) ;
Reimer; Jay; (Saint Paul, MN) ; Ahmann; Katherine
A.; (Arden Hills, MN) ; Panus; David A.;
(Maple Grove, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
St. Jude Medical, Cardiology Division, Inc. |
St. Paul |
MN |
US |
|
|
Assignee: |
St. Jude Medical, Cardiology
Division, Inc.
St. Paul
MN
|
Family ID: |
63013098 |
Appl. No.: |
16/023436 |
Filed: |
June 29, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62526492 |
Jun 29, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61L 27/3695 20130101;
A61L 27/507 20130101; A61L 2400/02 20130101; A61L 2430/40 20130101;
A61F 2/24 20130101; A61L 27/3687 20130101 |
International
Class: |
A61L 27/36 20060101
A61L027/36; A61L 27/50 20060101 A61L027/50; A61F 2/24 20060101
A61F002/24 |
Claims
1. A method of preparing calcification-resistant tissue,
comprising: providing fresh biological tissue; cross-linking the
tissue to produce fixed tissue; treating the fixed tissue with an
alcohol for a time sufficient to allow the alcohol to be diffused
into the tissue to produce alcohol-treated fixed tissue; and
treating the alcohol-treated fixed tissue with a polyol for a time
sufficient to allow fluid in the tissue to be replaced by the
polyol to produce alcohol/polyol-treated fixed tissue.
2. The method of claim 1, further comprising sterilizing the fixed
tissue in a solution comprising propylene oxide or peracetic acid
prior to the step of treating the fixed tissue with the
alcohol.
3. The method of claim 1, further comprising sterilizing the
alcohol/polyol-treated fixed tissue in a solution comprising
propylene oxide or peracetic acid.
4. The method of claim 1, further comprising: drying the
alcohol/polyol-treated fixed tissue to produce dried tissue; and
storing the dried tissue in a dry, ambient environment.
5. The method of claim 4, further comprising placing the dried
tissue in a package and sealing the package.
6. The method of claim 5, further comprising sterilizing the
package after the sealing step.
7. The method of claim 6, wherein the sterilization step is
performed by exposing the sealed package to ethylene oxide or
peracetic acid.
8. The method of claim 1, wherein the cross-linking step is
performed by using a glutaraldehyde or formaldehyde aqueous
solution.
9. The method of claim 1, wherein the alcohol is a lower aliphatic
(C.sub.1 to C.sub.8) alcohol, or a combination of lower aliphatic
alcohols.
10. The method of claim 1, wherein the alcohol is ethanol.
11. The method of claim 1, wherein the alcohol is in an aqueous
solution comprising from about 85 v/v % to about 100 v/v % of
alcohol.
12. The method of claim 1, wherein the step of treating the fixed
tissue with an alcohol is performed for about 12 hours to about 48
hours.
13. The method of claim 1, wherein the step of treating the fixed
tissue with an alcohol is performed at a temperature between about
15.degree. C. and about 30.degree. C.
14. The method of claim 1, wherein the polyol is a lower aliphatic
diol or triol (C.sub.1 to C.sub.4), or a combination of lower
aliphatic diols or triols.
15. The method of claim 1, wherein the polyol is glycerol.
16. The method of claim 1, wherein the polyol is in water or a 0.9
wt % aqueous saline solution comprising from about 20 v/v % to
about 100 v/v % of polyol.
17. The method of claim 1, wherein the step of treating the
alcohol-treated fixed tissue with a polyol is performed for about
12 hours to about 48 hours.
18. The method of claim 1, wherein the step of treating the
alcohol-treated fixed tissue with a polyol is performed at a
temperature between about 15.degree. C. and about 30.degree. C.
19. The method of claim 1, wherein the tissue is in the form of a
tissue component, a valve assembly for a bioprosthetic valve or a
fully assembled bioprosthetic valve incorporating the tissue.
20. Tissue prepared according to the method of claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of the filing
date of U.S. Provisional Patent Application No. 62/526,492 filed
Jun. 29, 2017, the disclosure of which is hereby incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present disclosure is directed to prosthetic medical
devices, in particular, prosthetic heart valves. More particularly,
the present disclosure is directed to prosthetic heart valves
formed from biological tissue, and to the treatment of such tissue
to resist calcification.
[0003] Bioprosthetic tissue is often used in bioprosthetic devices
or to repair damaged tissue in a patient. For example, it has
become common practice to replace damaged or diseased native heart
valves with bioprosthetic valves. The bioprosthetic valve, which is
also generally known as a "tissue valve," may be made with tissue
of biological origin, such as tissue of porcine or bovine origin.
Such valves are less likely to cause blood clotting and have
improved hemodynamic properties compared to mechanical valves that
may be made of metal or synthetic polymeric materials.
[0004] The most common cause for the failure of implanted
bioprosthetic devices is in vivo calcification. The mechanism of
calcification of bioprosthetic tissue is not fully understood.
Calcification may be due to host factors, implant factors, and
extraneous factors such as mechanical stress. Certain components
within the bioprosthetic tissue, such as phospholipids,
cholesterol, collagen and elastin, are known to be susceptible to
calcification. They can become calcified following the implantation
of bioprosthetic valves. The calcification can result in
undesirable stiffening or degradation of the bioprosthesis, which
leads to device failure.
[0005] Typically prior to implantation, the biological tissue is
chemically cross-linked or fixed with agents such as glutaraldehyde
or formaldehyde in order to prevent rejection when implanted into a
recipient, to provide sterilization, and to help stabilize the
proteins in the tissue, thereby making the tissue and the
bioprosthetic device containing such tissue more durable to
withstand prolonged use and millions of cycles of opening and
closing under circulatory pressure without fatigue. Glutaraldehyde
is the most commonly used fixative that can be applied at a
physiological pH under aqueous conditions for preparing tissue for
implantation. Unfortunately, glutaraldehyde is now known to promote
in vivo calcification. The unstable glutaraldehyde creates
potential calcium binding sites within the tissue that can lead to
calcification.
[0006] Various techniques have been developed in the treatment of
bioprosthetic tissue for mitigating in vivo calcification. One such
attempt, disclosed in U.S. Pat. No. 5,002,566 to Carpentier et al.,
involves a pretreatment of glutaraldehyde-fixed bioprosthetic
tissue with a calcification-inhibiting amount of ferric or stannic
ions or a mixture thereof. The CARPENTIER-EDWARDS ThermaFix.TM.
tissue process is an FDA-approved anti-calcification treatment of
bioprosthetic tissue that reduces the calcium binding sites by a
two-step process, with a first thermal treatment to remove up to 81
percent of the unstable glutaraldehyde and a second chemical
treatment to remove 98 percent of the phospholipids. In U.S. Pat.
No. 5,476,516, Seifter et al. disclose a method of treating
aldehyde-fixed biological tissue with a liquid polyol to minimize
in vivo calcification. The polyol is at least 60% in a solution,
and preferably solvent-free. Levy et al., in U.S. Pat. No.
5,746,775, discloses a tissue anti-calcification process for a
collagenous biomaterial in which the biomaterial is exposed to an
alcohol to inhibit calcification. The biomaterial, preferably
glutaraldehyde-pretreated, is subjected to an aqueous solution of
60% to 80% of a lower aliphatic alcohol, such as ethanol, for a
period of at least 20 minutes, and preferably, 24 to 72 hours. The
biomaterial is then rinsed, and stored in a glutaraldehyde solution
or ethanol-glutaraldehyde solution. This process reduces the
toxicity of glutaraldehyde, and removes 99 percent of the
cholesterol and 94 percent of the phospholipids in bioprosthetic
tissue, resulting in resistance to calcification in various
preclinical models.
[0007] To prevent the transmission of disease-causing
microorganisms to the device recipient, the tissue and the
bioprosthetic device made therefrom should be sterile. The
bioprosthetic device should be stored in a sterile and stable
condition from manufacture until use. For example, bioprosthetic
heart valves, including surgical and transcatheter heart valves,
are typically sterilized and stored in an aldehyde solution (i.e.,
glutaraldehyde or formaldehyde) prior to use. These solutions help
keep the tissue in a hydrated state and kill any microbes that may
be attached to the tissue. However, both glutaraldehyde and
formaldehyde are irritants and have some inherent level of
toxicity. Glutaraldehyde is also known to contribute to in vivo
calcification. A bioprosthetic device that is stored in such a
solution therefore must be extensively rinsed to remove any
residual aldehydes prior to implantation.
[0008] Attempts have been made to develop a bioprosthetic valve
that is in a substantially "dry" form, substantially free of
glutaraldehyde or formaldehyde, and ready for implantation with
minimal preparation prior to surgery. Chen et al., in U.S. Pat. No.
6,534,004, disclose a process for dry storing bioprosthetic devices
comprising a tissue component. The process includes treating the
fixed tissue component with an aqueous solution comprising
dimensional stabilizers such as polyhydric alcohols or their
derivatives. Another strategy, described in U.S. Pat. No. 8,748,490
to Dove et al., is to dehydrate the bioprosthetic tissue in a
glycerol/ethanol mixture. However, such dehydration processes do
not provide the tissue with calcification resistance.
[0009] Bioprosthetic tissue in the "dry" form is usually sterilized
with ethylene oxide, gamma irradiation, or electron beam
irradiation. However, ethylene oxide sterilization requires the
tissue to be exposed to increased temperatures and water vapor
which may damage or rehydrate the tissue. Gamma irradiation is
known to cause backbone scission and breakage of collagen fibrils,
leading to decreased mechanical and biochemical functionality in
the tissue. Electron beam irradiation will also cleave the collagen
backbone and lead to deterioration of the tissue structure and
reactivity. These types of damage during sterilization and/or
storage may contribute to valve deterioration and structural
failure.
[0010] Therefore, there is a continuing need to develop a method of
preparing bioprosthetic tissue or a bioprosthetic device containing
such tissue so as to minimize in vivo calcification and allow for
sterilization and storage in a non-toxic environment without
causing damage to the tissue.
BRIEF SUMMARY OF THE INVENTION
[0011] The present disclosure relates to methods of preparing
calcification-resistant bioprosthetic tissue or a bioprosthetic
device containing such tissue, wherein the tissue, preferably
pre-fixed bioprosthetic tissue, is treated with a two-step process,
an alcohol treatment followed by exposure to a polyol. The two-step
treatment process minimizes in vivo calcification and reduces
cytotoxicity without impairing the mechanical strength of the fixed
bioprosthetic tissue. The processed tissue when wet may be
sterilized and/or stored using an appropriate method that is
compatible with the wet tissue. Preferably, the processed wet
tissue may be sterilized and stored in a non-toxic solution
containing propylene oxide (which converts to non-toxic propylene
glycol during sterilization and storage).
[0012] The process preferably further comprises the step of drying
the alcohol/polyol-treated fixed tissue at ambient conditions or
under vacuum, and the resultant tissue or device made therefrom can
be stored in a dry ambient condition. These methods thus provide
the advantages of producing tissue or devices containing such
tissue with reduced size, volume and weight compared to
bioprosthetic tissue or devices stored in a fluid medium;
eliminating toxic fluid associated with the tissue or device
storage; and reducing changes or damage to the tissue during the
drying process. The processed tissue when dried may be sterilized
using an appropriate method that is compatible with the dry tissue.
Preferably, the processed dry tissue may be sterilized by exposure
to ethylene oxide gas or peracetic acid gas. Prior to use, the
tissue or the device comprising the same is optionally rinsed or
rehydrated, such as by a sterile 0.9 wt % aqueous saline
solution.
[0013] The present disclosure describes methods of preparing
biological tissue that is resistant to in vivo calcification, and
therefore has good mechanical stability and durability. The tissue
is for use in bioprosthetic devices or other heterograft
applications. In one embodiment, the bioprosthetic device is a
bioprosthetic heart valve.
[0014] In one embodiment, the method comprises the steps of fixing
fresh biological tissue; treating the fixed tissue with an alcohol
for a time sufficient to allow the alcohol to be diffused into the
tissue; and treating the alcohol-treated fixed tissue with a polyol
for a time sufficient to allow the fluid in the tissue to be
replaced by the polyol. The alcohol is preferably a lower aliphatic
alcohol (C.sub.1 to C.sub.8) which includes, but is not limited to,
methanol, ethanol, propanol, isopropanol, pentanol, octanol, or a
combination thereof. More preferably, the alcohol is ethanol. The
alcohol is preferably in an aqueous solution comprising from about
85 v/v % to about 100 v/v % of alcohol (i.e., a neat alcohol); and
more preferably, about 95 v/v % of alcohol. The polyol is
preferably a lower aliphatic diol or triol (C.sub.1 to C.sub.4)
which includes, but is not limited to, ethylene glycol, propylene
glycol, butylene glycol, glycerol, or a combination thereof. More
preferably, the polyol is glycerol. The polyol is preferably in a
0.9 wt % aqueous saline solution comprising about 20 v/v % to about
100 v/v % of polyol (i.e., a neat polyol), and more preferably,
about 50 v/v % of polyol. In one embodiment, the
alcohol/polyol-treated fixed tissue is stored in an aqueous
solution. The processed tissue when wet may be sterilized using an
appropriate sterilization method that is compatible with wet
tissue.
[0015] Preferably, the method further comprises placing the
alcohol/polyol-treated fixed tissue at an ambient condition or
under vacuum for drying; and storing the dried tissue in a dry
ambient condition. In another embodiment, the processed tissue when
dried may be sterilized using an appropriate sterilization method
that is compatible with dry tissue.
[0016] The tissue may be in the form of a tissue component for a
bioprosthetic device or other heterograft applications. The device
may be a valve assembly for a bioprosthetic heart valve, or a fully
assembled bioprosthetic heart valve incorporating the tissue.
[0017] The present disclosure also relates to tissue, a
bioprosthetic device or a packaged bioprosthetic device containing
the same, wherein the tissue is prepared by the processing methods
described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These and other features, aspects, and advantages of the
present disclosure will become better understood with regard to the
following description, appended claims, and accompanying drawings
in which:
[0019] FIG. 1 is a bar graph depicting the mean calcium of Test
Groups 1-6 in a 63-day rat subdermal study; and
[0020] FIG. 2 is a bar graph depicting the mean calcium of Test
Groups 1-6 with the folded samples removed in a 63-day rat
subdermal study.
DETAILED DESCRIPTION
[0021] Before describing at least one embodiment of the present
disclosure in detail, it is to be understood that the present
disclosure is not limited in its application to the details set
forth in the following description or exemplified by the examples.
Aspects of the present disclosure are capable of other embodiments
or of being practiced or carried out in various ways. Also, it is
to be understood that the phrasing and terminology employed herein
is for the purpose of description and should not be regarded as
limiting.
[0022] The present disclosure provides a method of preparing
bioprosthetic tissue or a bioprosthetic device comprising such
tissue so as to have strong calcification resistance and allow for
sterilization and storage in a non-toxic environment without
causing damage to the tissue. Bioprosthetic valves, which are also
generally known as "tissue valves," are prosthetic valves made with
at least some tissue of biological origin. "Biological tissue" or
"tissue," as used herein, refers to biological tissue dissected
from an animal, typically a mammalian species such as, for example,
porcine or bovine tissue. Specific tissue types that may be used
include, without limitation, any blood vessel, pericardial tissue,
heart muscle tissue, dura matter and the like. More than one
species and tissue type may be used in a valve assembly. "Fixed" or
"cross-linked" tissue refers to tissue in which the proteins have
reduced solubility, antigenicity, and biodegradability as compared
to the proteins in the native tissue. "Fixing" or "cross-linking"
can be accomplished by a number of techniques, for example, by
treatment with aldehydes, epoxides, carbodimides or genipin, or by
photo fixation. Conventionally, fixing can be performed by
cross-linking the amine groups of the tissue proteins with an
aldehyde, such as about 0.001 v/v % to about 5 v/v % glutaraldehyde
or formaldehyde solution. The term "valve" as used herein refers to
a complete and operable structure capable of being implanted into a
patient to control the flow of blood through the patient's
circulatory system. A valve can be a surgical valve, a
transcatheter valve or any other non-native (i.e., prosthetic)
valve structure. The terms "implanted" or "implantation," as used
herein, refer to a complete and long-term seating of a valve in a
patient. A "valve assembly" as used herein is a structure that is
made, at least in part, from tissue, and that operates to meter or
restrict blood flow for at least some period of time, but does not
include other structures like a stent often used to support the
valve assembly. Thus, a tissue valve for purposes of the present
description is a bioprosthetic valve that includes at least a valve
assembly. The tissue valve may, and often does, include other
structures, such as a supporting stent. As used herein, the terms
"about," "generally," "substantially" and the like are intended to
mean that slight deviations from absolute are included within the
scope of the term so modified. Bioprosthetic valves in accordance
with the present disclosure may be used in the heart as a
replacement for one of the native cardiac valves, such as the
aortic valve or mitral valve, but are not limited thereto and can
be used in other structures, including blood vessels.
[0023] In one embodiment, fresh biological tissue is first fixed or
crossed-linked. Fixing or cross-linking can be accomplished by a
number of techniques, for example, by cross-linking with epoxides,
carbodimides or genipin, or photo fixation. Conventionally, fixing
can be accomplished by cross-linking the amine groups of the tissue
proteins with an aldehyde, such as a solution of about 0.001 v/v %
to about 5 v/v %, preferably about 0.2 v/v % to about 0.8 v/v %,
more preferably about 0.5 v/v %, of glutaraldehyde or formaldehyde
in a solvent for about several hours to several weeks. In some
embodiments, the solvent may be water or a 0.9 wt % aqueous saline
solution. In other embodiments, the solvent may be either a
phosphate-buffered solution such as phosphate-buffered saline
(PBS), or preferably, a phosphate-free buffer. Phosphate-free
buffers include, but are not limited to, borate, carbonate,
bicarbonate, citrate, cacodylate, and other synthetic buffers such
as N-2-Hydroxyethylpiperazine-N'-2-ethanesulphonic acid (HEPES),
2-(N-morpholino)-propane-sulphonic acid (MOPS) and
1,4-piperazinebis(Ethanesulphonic acid) (PIPES). Glutaraldehyde is
the most commonly used fixative that can be applied at a
physiological pH under aqueous conditions for preparing tissues for
implantation. In one embodiment, the fresh biological tissue may be
exposed to a glutaraldehyde solution in a preferred concentration
noted above at a temperature from about 4.degree. C. to about
25.degree. C. and a pH from about 6 to about 8, preferably from
about 7.1 to about 7.8. The fixed tissue is optionally rinsed
thoroughly with a sterile 0.9 wt % aqueous saline solution to
substantially reduce the amount of unreacted fixative within the
tissue. Thereafter, the fixed tissue is further processed
immediately or stored in an aqueous solution until further
processing to prevent drying out and shrinkage of the fixed
tissue.
[0024] In one embodiment, the aqueous storage solution may comprise
about 0.001 v/v % to about 10 v/v %, preferably about 0.5 v/v %, of
glutaraldehyde or formaldehyde. In another embodiment, the aqueous
storage solution may be sterile saline. A saline solution is
generally composed of distilled and/or deionized water with sodium
chloride in a concentration ranging from about 0.01 wt % to about
1.5 wt %. More specifically, the sodium chloride concentration can
range from about 0.75 wt % to about 1.05 wt %, and preferably is
about 0.9 wt %. Isotonic saline is often used. As an alternative to
sodium chloride, the following salts may be used for the saline
solution: potassium chloride, calcium chloride, magnesium sulfate,
disodium phosphate, sodium bicarbonate, magnesium chloride, sodium
phosphate, potassium phosphate, or any combination thereof, with or
without sodium chloride. Additionally, the saline solution may be a
balanced salt solution such as Hank's, Earle's, Gey's or Ouck's
balanced salt solution, or may be a phosphate buffered solution.
Treating the tissue with a saline solution may assist in leaching
organic solvents or residue from the tissue.
[0025] After the fixing step (or after removal from the aqueous
storage solution), the tissue optionally can be sterilized using an
appropriate method that is compatible with the wet tissue. Such
method includes, but is not limited to, using various solutions,
such as aldehydes, alcohols, epoxides, a combination thereof, or
other various antimicrobial solutions, for liquid chemical
sterilization. In one embodiment, the processed wet tissue can be
sterilized and stored in a standard aldehyde solution, such as a
glutaraldehyde or formaldehyde solution that is typically used for
long-term sterilization and storage of clinical-grade
bioprostheses, preferably at a concentration of about 0.2 v/v % to
about 0.8 v/v %, more preferably at a concentration of about 0.5
v/v % of aldehyde in water, in a 0.9 wt % aqueous saline solution,
in a phosphate-buffered solution, or in a phosphate-free buffered
solution. In one preferred embodiment, the processed wet tissue can
be sterilized and stored in a solution containing propylene oxide
or peracetic acid. The solution may include propylene oxide or
peracetic acid in buffered or unbuffered water or in a 0.9 wt %
aqueous saline solution. Propylene oxide is more biocompatible
compared to conventional antimicrobial solutions containing
aldehydes. The propylene oxide solution is preferably a solution
containing about 1% to about 10% propylene oxide, preferably about
2% propylene oxide. In one embodiment, the sterilization and
storage solution is buffered to a pH between about 6.0 and about
8.0, and preferably between about 7.1 and about 7.8, and more
preferably about 7.4. Suitable buffers for use in these solutions
are those buffers that have a buffering capacity sufficient to
maintain a physiologically acceptable pH and that do not cause any
deleterious effects to the bioprosthetic tissue or interfere with
the treatment process. Exemplary buffers include, but are not
limited to, phosphate-buffered saline (PBS), and phosphate-free
buffers such as borate, carbonate, bicarbonate, citrate,
cacodylate, N-2-Hydroxyethylpiperazine-N'-2-ethanesulphonic acid
(HEPES), 2-(N-morpholino)-propane-sulphonic acid (MOPS) and
1,4-piperazinebis(Ethanesulphonic acid) (PIPES).
[0026] The fixed tissue (before or after sterilization) may be
treated with an alcohol. Preferably, the alcohol is a lower
aliphatic alcohol (C.sub.1 to C.sub.8) which includes, but is not
limited to, methanol, ethanol, propanol, isopropanol, pentanol,
octanol, or a combination thereof. More preferably, the alcohol is
ethanol. The manner in which the fixed tissue is exposed to the
alcohol includes, but is not limited to, vapor, plasma, liquid, and
cryogenic application of the alcohol. Preferably, the tissue is
treated with an alcohol solution. More preferably, the alcohol
solution is an aqueous solution comprising from about 85 v/v % to
about 100 v/v % of alcohol (i.e., a neat alcohol); and most
preferably, about 95 v/v % of alcohol. In one embodiment, the
aqueous alcohol solution may be buffered to a pH between about 6.0
and about 8.0, and preferably between about 7.1 and about 7.8, and
more preferably about 7.4. Suitable buffers for use in this step
are those buffers that have a buffering capacity sufficient to
maintain a physiologically acceptable pH and that do not cause any
deleterious effects to the bioprosthetic tissue or interfere with
the treatment process. Exemplary buffers include, but are not
limited to, phosphate-buffered saline (PBS), and phosphate-free
buffers such as borate, carbonate, bicarbonate, citrate,
cacodylate, N-2-Hydroxyethylpiperazine-N'-2-ethanesulphonic acid
(HEPES), 2-(N-morpholino)-propane-sulphonic acid (MOPS) and
1,4-piperazinebis(Ethanesulphonic acid) (PIPES).
[0027] The tissue component may be exposed to, or contacted with,
the alcohol for a time and at a temperature sufficient to permit
the alcohol to penetrate into the interstices of the tissue by
passive diffusion and replace the fluid therein. The time needed to
achieve such replacement is directly related to the thickness of
the tissue, and inversely related to the ratio between the volume
of the alcohol or alcohol solution and the volume of the tissue.
Tissue having a thickness between about 0.05 mm and about 2 mm may
be contacted with an alcohol solution at a temperature between
about 4.degree. C. and about 37.degree. C. for about 12 hours to
about 48 hours; preferably, for about 24 hours. More preferably,
such tissue may be contacted with an alcohol solution at room
temperature for about 24 hours.
[0028] The tissue may be contacted with the alcohol solution by a
standard method, such as by immersion in the solution. The amount
of the alcohol solution is at least sufficient to submerge the
tissue. Preferably, the volume of the alcohol solution is at least
about 2 times the volume of the tissue that is brought into contact
with the solution; more preferably, about 50 times the volume of
the tissue; and still more preferably, about 100 times the volume
of the tissue.
[0029] In one embodiment, the tissue may be shaken or agitated
during the alcohol treatment. Shaking can be accomplished in any
manner, such as through the use of an orbital shaker, or a shaker
stand.
[0030] After exposure to the alcohol for a sufficient time, the
tissue is removed from the alcohol and optionally rinsed with a
sterile 0.9 wt % aqueous saline solution. The alcohol-treated fixed
tissue may then be treated with a polyol. Preferably, the polyol is
a lower aliphatic diol or triol (C.sub.1 to C.sub.4) which
includes, but is not limited to, ethylene glycol, propylene glycol,
butylene glycol, glycerol, or a combination thereof. More
preferably, the polyol is glycerol. Preferably, the
alcohol-treated, fixed tissue is treated with a polyol solution.
The polyol may be in solution with water or with a 0.9 wt % aqueous
saline solution, and may comprise from about 20 v/v % to about 100
v/v % of polyol (i.e., a neat polyol); and preferably, about 50 v/v
% of polyol. A solution of polyol in a 0.9 wt % aqueous saline
solution is preferred. In one embodiment, a solution of polyol in
water may be buffered to a pH between about 6.0 and about 8.0,
preferably between about 7.1 and about 7.8, and more preferably
about 7.4. Suitable buffers for use are those buffers that have a
buffering capacity sufficient to maintain a physiologically
acceptable pH and that do not cause any deleterious effects to the
bioprosthetic tissue or interfere with the treatment process.
Exemplary buffers include, but are not limited to,
phosphate-buffered saline (PBS), and phosphate-free buffers such as
borate, carbonate, bicarbonate, citrate, cacodylate,
N-2-Hydroxyethylpiperazine-N'-2-ethanesulphonic acid (HEPES),
2-(N-morpholino)-propane-sulphonic acid (MOPS) and
1,4-piperazinebis(Ethanesulphonic acid) (PIPES).
[0031] The tissue component may be exposed to, or contacted with,
the polyol for a time and at a temperature sufficient to permit the
polyol to penetrate into the interstices of the tissue by passive
diffusion and replace the fluid therein. The time needed to achieve
such replacement is directly related to the thickness of the
tissue, and inversely related to the ratio between the volume of
the polyol or polyol solution and the volume of the tissue. Tissue
having a thickness between about 0.05 mm and about 2 mm may be
contacted with a polyol solution at a temperature between about
4.degree. C. and about 37.degree. C. for about 12 hours to about 48
hours; preferably, for about 24 hours. More preferably, such tissue
may be contacted with a polyol solution at room temperature for
about 24 hours.
[0032] The tissue may be contacted with the polyol solution by a
standard method, such as by immersion in the solution. The amount
of the polyol solution is at least sufficient to submerge the
tissue. Preferably, the volume of the polyol solution is at least
about 2 times the volume of the tissue that is brought into contact
with the solution; more preferably, about 50 times the volume of
the tissue; and still more preferably, about 100 times the volume
of the tissue. The tissue may be shaken or agitated in any manner
during the polyol treatment, such as the manners described above
for use during the alcohol treatment.
[0033] After soaking in the polyol solution for a sufficient time,
the tissue is removed from the polyol solution and optionally
rinsed with a sterile 0.9 wt % aqueous saline solution. It then may
be placed in an aqueous solution for storage until use. The aqueous
storage solution is described above. In one embodiment, the
alcohol/polyol-treated fixed tissue can be stored in a package with
an aqueous solution.
[0034] The treated, fixed, wet tissue (with or without
sterilization before the alcohol treatment step) may be sterilized
after the polyol treatment using an appropriate method that is
compatible with the wet tissue. Preferably, only if not sterilized
before the alcohol treatment step, the treated, fixed, wet tissue
may be sterilized after the polyol treatment using an appropriate
method that is compatible with the wet tissue. Any of the methods
described above for the sterilization of wet tissue after the
fixing step may be used.
[0035] Preferably, the method further comprises placing the
alcohol/polyol-treated fixed tissue in an ambient condition or
under vacuum for drying; and storing the dry tissue in a dry
ambient condition. The alcohol/polyol-treated fixed tissue may be
exposed to ambient air at a temperature from about 15.degree. C. to
about 25.degree. C. and a relative humidity from about 10% to about
30% for at least four hours to remove the aqueous solution.
Preferably, the alcohol/polyol-treated fixed tissue is exposed to
ambient air at room temperature for about 12 hours.
[0036] In one embodiment, the alcohol/polyol-treated fixed tissue
may be placed in a jar or other container for vacuum drying. Vacuum
drying is a process in which materials are dried in a reduced
pressure environment, which lowers the heat needed for rapid
drying. As such, vacuum-drying tends to retain the integrity of the
original item with less damage. A vacuum is applied to the
container having the tissue inside for a time sufficient to remove
substantially all the fluid in the tissue, without the application
of heat. The vacuum pressure is no more than about 1000 mTorr,
preferably no more than about 200 mTorr, and more preferably no
more than about 10 mTorr. The tissue can be subjected to vacuum
drying for about one minute to about 2 months. Preferably, a vacuum
of about 5 mTorr is applied to the container for at least 4 hours.
More preferably, a vacuum of about 5 mTorr is applied to the
container for about 6 to about 24 hours.
[0037] The alcohol/polyol treatment of the tissue and the drying
steps described above may be performed on individual tissue
components for the valve assembly, on a valve assembly, or on a
completed tissue valve. Thus, individual tissue components may be
subjected to the alcohol/polyol treatment steps before or after
formation of the valve assembly but prior to the fabrication of the
tissue valve, or after fabrication of the tissue valve. In one
embodiment, the individual tissue components may be tissue patches
for use in cardiac repairs. Such tissue patches prepared using the
alcohol/polyol treatment steps described herein may advantageously
have strong calcification resistance.
[0038] Air-drying or vacuum-drying of the alcohol/polyol-treated
fixed tissue can occur before or after construction of a valve
assembly or before or after construction of a tissue valve. Thus,
in one embodiment, the alcohol/polyol-treated "wet" fixed tissue
(bioprosthetic fixed tissue treated with an alcohol followed by a
polyol) may be air-dried or vacuum-dried and then stored dry until
needed for manufacture. The tissue may be rehydrated prior to being
manufactured into a valve assembly, and may then be air-dried or
vacuum-dried again for storage. In another embodiment, the
alcohol/polyol-treated "wet" fixed tissue may be attached to a
support or stent to construct a valve assembly on the support and
thereafter the entire resulting tissue valve may be air-dried or
vacuum-dried prior to storage. In yet another embodiment, the
alcohol/polyol-treated "wet" fixed tissue may be used to construct
a "wet" valve assembly without a support. This "wet" valve assembly
can be stored in an aqueous solution. It can also be air-dried or
vacuum-dried, and then attached to a support; or attached to the
support first, followed by air-drying or vacuum-drying of the
resulting tissue valve.
[0039] The construction of a valve assembly or a tissue valve can
involve general techniques used in the art. An example of a method
of constructing a tissue valve includes attaching a valve assembly
comprised of at least one leaflet to a support or stent configured
to fit within the relevant structure within the patient. The
support could either have a fixed size in the case of a surgical
valve, or could be collapsible in the case of a transcatheter valve
implanted using a minimally invasive procedure.
[0040] Due to the removal of fluid from the bioprosthetic tissue
during the air-drying or vacuum-drying process, the resulting "dry"
bioprosthetic valve has a reduced size, volume and weight when
compared to a tissue valve that was stored in a fluid medium.
Normally, the weight of "dry" bioprosthetic tissue is at least
about 50%, preferably about 75-80%, less than the weight of the
same tissue in the wet state.
[0041] The method of producing tissue valves for dry storage in the
present application eliminates the use of toxic fluids associated
with the storage of valves and the subsequent rinsing process,
which may make the manufacture and transport of the valves less
expensive, may make storage and use more convenient, and may result
in less chemical waste to dispose of. It also may reduce the time
spent in the operating room preparing the tissue valve for
implantation.
[0042] Since the tissue valves prepared by the methods described
herein do not need to be shipped or stored in a solution to prevent
the tissue from drying out, they may be preloaded onto delivery
devices, with the entire assembly being provided in sterile
packaging such that the valves are able to be reconstituted before
use.
[0043] The dry tissue component, or the valve assembly or
bioprosthetic valve comprising the dry tissue component, wherein
the tissue has been treated with alcohol after fixing followed by
polyol treatment, may be stored in an environment essentially free
of liquid for later processing or implantation. An environment,
container or package that is "essentially free of liquid" as used
herein means an environment in which the presence of water or other
liquids is limited to the content of such liquids in the ambient
air (as more precisely expressed as the relative humidity), and the
content of liquid contained within the treated tissue disposed
within the container or package. Preferably, the treated dry tissue
component, valve assembly or bioprosthetic valve made therefrom is
placed into a microorganism-resistant package. An example of a
packaged tissue valve ready for reconstitution includes a package
having an outer periphery that defines an inner space. The inner
space has an environment that is substantially dry and sterile. The
tissue valve includes a support configured to fit within the inner
space of the package and a vacuum-dried or lyophilized valve
assembly attached to the support. The dry tissue valve is encased
within the package. In one embodiment, the package with the dry
tissue valve may also include a delivery device. In another
embodiment, the dry tissue valve may be preloaded within the
delivery device within the package.
[0044] After the dry tissue component, valve assembly or
bioprosthetic valve has been placed in the inner space of the
package, the package may be sealed. The sealed package may then be
sterilized, such as by a gas sterilization process or by exposure
to ionizing radiation. The gas sterilization process involves
exposure to a gas including, but not limited to, ethylene oxide and
peracetic acid. The ionizing radiation can be gamma irradiation or
electron beam irradiation. To ensure the inner space remains
sterile following sterilization, the package is preferably formed
from a material, such as Tyvek.RTM. (E.I. DuPont de Nemours and
Company) or Mylar.RTM. (DuPont Teijin Films U.S.), which is
impenetrable to microorganisms such as bacteria and fungi.
[0045] An example of a conventional procedure for sterilization by
exposure to ethylene oxide involves exposure of the package to a
mixture of 10 wt % ethylene oxide and 90 wt %
hydrochlorofluorocarbon at a chamber pressure of about 8 to about
10 psi and a temperature of about 38.degree. C. for about 24 hours,
or a temperature of about 54-57.degree. C. for about 130 minutes.
In one embodiment, the package may be exposed to 100 wt % of
ethylene oxide gas at a chamber pressure of about 1.3 psi, a
relative humidity of about 50% and a temperature of about
40.degree. C. for about 12 hours.
[0046] In one preferred embodiment, the sealed package may be
sterilized by exposure to peracetic acid gas. The mechanism of
action of peracetic acid is thought to be similar to other
oxidizing agents, i.e., it denatures proteins, disrupts cell wall
permeability, and oxidizes sulfhydral and disulfide bonds in
proteins, enzymes, and other metabolites. The peracetic acid vapor
interacts with numerous cellular constituents, breaking them down
and inactivating routine functionality. With the disintegration of
the bacterial cell wall, internal components will no longer be
contained and are unable to organize. Proteins are rapidly attacked
by peracetic acid through oxidation of amino acids to carbonyls,
particularly tryptophan, cysteine and methionine. Sterilization by
peracetic acid can be performed in a chamber of 500 Torr at room
temperature (18-30.degree. C.) for a short period of time, for
example, a few seconds to a few hours. Compared to conventional
sterilization by ethylene oxide, gamma irradiation or electron beam
irradiation, peracetic acid sterilization provides high
compatibility with materials, low temperature operation that does
not affect the product or packaging, low or no residuals, safety to
use for operators, and short processing times.
[0047] The resulting product is a substantially sterile tissue
component, valve assembly or implantable tissue or bioprosthetic
valve suitable for dry storage. The sterile bioprosthetic tissue
valve prepared in accordance with the present methods may be
well-suited for implantation into patients with cardiovascular
diseases. As used herein, the term "patient" means any mammals such
as, for example, humans, dogs, cats, horses, and non-human
primates. Prior to use, the bioprosthetic valve is removed from the
package, and the tissue portion thereof may be rehydrated by
exposure to an aqueous solution, preferably a sterile saline
solution, such as a sterile 0.9 wt % aqueous saline solution. In
some instances, the tissue portion may be rehydrated by rinsing
with a sterile 0.9 wt % aqueous saline solution for about two to
about ten seconds, and the valve may then be loaded into or onto a
delivery device. When a substantially sterile tissue component or
valve assembly is stored in the package, the tissue component or
valve assembly may be rehydrated using the same technique as for
the bioprosthetic valve, after which the tissue component or valve
assembly may be assembled to a support to form a bioprosthetic
valve.
[0048] Rehydration or reconstitution of the vacuum-dried or
lyophilized tissue before use may be a complete reconstitution in
which the moisture content of the tissue is roughly equivalent to
the moisture content the tissue would have when in equilibrium with
the patient's biofluid in situ. In such circumstances, and in some
embodiments, the delivery device may be configured to accommodate a
resulting increase in the volume of the rehydrated bioprosthetic
valve, if needed.
[0049] In one embodiment, the tissue valve comprises a vacuum-dried
or lyophilized valve assembly attached to a stent that is capable
of being resheathed, with the resulting tissue valve loaded onto a
delivery device which permits resheathing. The stent and the valve
assembly are configured cooperatively such that the valve assembly
can be exposed when on the delivery device, reconstituted,
sheathed/resheathed and/or implanted. This allows the surgical team
to expose the valve assembly for reconstitution prior to
implantation. In a further aspect of this embodiment, the stent may
be structured such that the valve assembly can be exposed for
reconstitution. In another embodiment, a bioprosthetic valve may be
partially preloaded onto a delivery device to allow rehydration. In
a further embodiment, a bioprosthetic valve which is not preloaded
onto a delivery device may be reconstituted and thereafter crimped
and loaded onto a delivery device.
[0050] In another embodiment, the valve assembly may be
reconstituted while fully sheathed. Reconstitution while fully
sheathed may be achieved by irrigating an aqueous solution through
the delivery device prior to implantation.
[0051] Described herein are methods of preparing bioprosthetic
tissue or a bioprosthetic device comprising the same so as to have
strong calcification resistance and allow for sterilization and
storage in a non-toxic environment without causing damage to the
tissue. The methods comprise fixing the tissue, treating the fixed
tissue with an alcohol solution and subsequently with a polyol
solution, air-drying or vacuum-drying of the alcohol/polyol-treated
fixed tissue, and sterilizing the dried tissue. As a result, tissue
treated in accordance with the present methods can be returned to a
size that is at least about 90%, preferably at least about 95%,
more preferably at least about 98%, of its original hydrated size
following rehydration in sterile saline for about 10 seconds.
Tissue prepared in accordance with the present methods is therefore
well-suited for use in a bioprosthetic valve.
[0052] The following examples are for purpose of illustration only
and are not intended to limit the scope of the disclosure as
defined in the claims hereinafter.
[0053] Bovine pericardial tissue that was freshly pre-fixed with
0.5 v/v % of gluaraldehyde in a PBS buffer was used in the test
groups set forth below.
[0054] Test Group 1
[0055] The pre-fixed tissue was sterilized by a typical process
according to a manufacturing standard, rinsed with a sterile 0.9 wt
% aqueous saline solution for about 20 minutes, and preserved in a
0.5 v/v % formaldehyde phosphate-buffered solution. Before
implantation, ten tissue specimens were removed from the 0.5 v/v %
formaldehyde phosphate-buffered preservation solution, and rinsed
with a sterile 0.9 wt % aqueous saline solution for 2-10 seconds.
Test Group 1 was for a positive calcium control.
[0056] Test Group 2
[0057] The pre-fixed tissue was sterilized by a typical process
according to a manufacturing standard, and rinsed with a sterile
0.9 wt % aqueous saline solution for about 20 minutes. Ten
resulting tissue specimens were then immersed in a 95 v/v % ethanol
aqueous solution for about 24 hours. The tissue specimens were
removed from the ethanol solution and rinsed with a sterile 0.9 wt
% aqueous saline solution for about 20 minutes. The tissue
specimens were then stored in a 0.5 v/v % formaldehyde
phosphate-buffered solution. Before implantation, tissue specimens
were removed from the 0.5 v/v % formaldehyde phosphate-buffered
preservation solution and rinsed with a sterile 0.9 wt % aqueous
saline solution for 2-10 seconds.
[0058] Test Group 3
[0059] The pre-fixed tissue was sterilized by a typical process
according to a manufacturing standard, and rinsed with a sterile
0.9 wt % aqueous saline solution for about 20 minutes. Ten
resulting tissue specimens were then immersed in a 95 v/v % ethanol
aqueous solution for about 24 hours. The tissue specimens were
removed from the ethanol solution and rinsed with a sterile 0.9 wt
% aqueous saline solution for about 20 minutes. The tissue
specimens were subsequently immersed in a 50 v/v % glycerol in a
0.9 wt % aqueous saline solution for about 24 to about 26 hours.
The tissue specimens were removed from the glycerol solution and
then air-dried at room temperature of about 25.degree. C. for about
16 to about 24 hours. The dried tissue specimens were put in a jar
sealed with a Tyvek.RTM. membrane for sterilization. The sealed jar
was exposed to 100 wt % of ethylene oxide (EO) gas at a chamber
pressure of about 1.3 psi and relative humidity of about 50% and a
temperature of about 40.degree. C. for about 12 hours. The tissue
specimens were stored in the jar at ambient conditions. Before
implantation, the valve specimens were rinsed with a sterile 0.9 wt
% aqueous saline solution for 2-10 seconds.
[0060] Test Group 4
[0061] Ten tissue specimens were prepared according to Test Group
3, except that before implantation, the tissue specimens were not
rinsed.
[0062] Test Group 5
[0063] Ten tissue specimens were prepared according to Test Group
3, except that the dried tissue specimens were put in a jar sealed
with a Mylar.RTM. membrane for sterilization with peracetic acid
(PAA). The jar was exposed to 100 wt % of peracetic acid gas at a
chamber pressure of about 500 Torr at room temperature of about
25.degree. C. for about 15 minutes.
[0064] Test Group 6
[0065] Ten tissue specimens were prepared according to Test Group
5, except that before implantation, the tissue specimens were not
rinsed.
[0066] The preparation of the specimens for Test Groups 1-6 are
summarized in Table 1 as follows:
TABLE-US-00001 TABLE 1 Processes for Test Groups 1-6 Terminal Pre-
Test Sample Anti-calcification Sterilization Implant Group #
Numbers Treatment Drying Method Rinse 1 10 None None None Yes 2 10
Ethanol None None Yes 3 10 Ethanol/Glycerol Yes EO Yes 4 10
Ethanol/Glycerol Yes EO No 5 10 Ethanol/Glycerol Yes PAA Yes 6 10
Ethanol/Glycerol Yes PAA No
[0067] The tissue specimens of Test Groups 1-6 were then implanted
into a subcutaneous pocket in 3-4 week old Sprague-Dawley rats. At
the end of a period of 63 days, the tissue specimens were collected
and examined for calcification by quantitative analyses of calcium
and phosphorus using Inductively Coupled Plasma Optical Emission
Spectrometry (ICP-OES). The mean calcium results are summarized in
Table 2 below and in FIG. 1.
TABLE-US-00002 TABLE 2 ICP Calcium Results Sample Test Group #
Numbers Mean Calcium (mg/g) 1 10 193.31 .+-. 18.30 2 10 2.14 .+-.
6.35 3 10 0.11 .+-. 0.01 4 10 10.89 .+-. 34.11 5 10 23.40 .+-.
43.14 6 10 9.49 .+-. 29.69 *data represented as mean +/- one
standard deviation
[0068] Table 2 and FIG. 1 demonstrate that a two-step treatment of
bioprosthetic tissue first with ethanol followed by glycerol
greatly minimizes the calcification.
[0069] Several of the test specimens were identified as folded
during sample recovery at term. Folded tissue can potentially cause
stress-induced calcification and increase the variability in the
test results. Approximately 40% of the folded test samples were
calcified, and 100% of the folded samples were calcified in both
Test Group 1 (control group) and Test Group 2. Because the calcium
in these samples was likely related to the folded (stressed)
condition of the samples, the folded sample results (including
samples that did not calcify) were removed as "outliers" and the
data was re-evaluated. The mean calcium results are summarized in
Table 3 below and in FIG. 2:
TABLE-US-00003 TABLE 3 ICP Calcium Results Sample Test Group #
Numbers Mean Calcium (mg/g) 1 8 200.71 .+-. 8.62 2 9 0.13 .+-. 0.02
3 9 0.11 .+-. 0.01 4 8 0.09 .+-. 0.01 5 7 4.44 .+-. 11.49 6 6 0.10
.+-. 0.01 *data represented as mean +/- one standard deviation
[0070] It is interesting to note that the majority of folded
samples did not calcify in Test Groups 3-6. The two-step
ethanol/glycerol process used for Test Groups 3-6 may help reduce
stress-induced calcification.
[0071] To summarize the foregoing description, a method of
preparing calcification-resistant tissue includes providing fresh
biological tissue; cross-linking the tissue to produce fixed
tissue; treating the fixed tissue with an alcohol for a time
sufficient to allow the alcohol to be diffused into the tissue to
produce alcohol-treated fixed tissue; and treating the
alcohol-treated fixed tissue with a polyol for a time sufficient to
allow fluid in the tissue to be replaced by the polyol to produce
alcohol/polyol-treated fixed tissue; and/or
[0072] the method may further include storing the
alcohol/polyol-treated fixed tissue in an aqueous solution;
and/or
[0073] the method may further include sterilizing the
alcohol/polyol-treated fixed tissue in a solution comprising
propylene oxide or peracetic acid; and/or
[0074] the method may further include drying the
alcohol/polyol-treated fixed tissue to produce dried tissue, and
storing the dried tissue in a dry, ambient environment; and/or
[0075] the method may further include placing the dried tissue in a
package and sealing the package; and/or
[0076] the method may further include sterilizing the fixed tissue
in a solution comprising propylene oxide or peracetic acid prior to
the step of treating the fixed tissue with the alcohol; and/or
[0077] the method may further include sterilizing the package after
the sealing step; and/or
[0078] the sterilization step may be performed by exposing the
sealed package to ethylene oxide or peracetic acid; and/or
[0079] the cross-linking step may be performed by using a
glutaraldehyde or formaldehyde aqueous solution; and/or
[0080] the alcohol may be a lower aliphatic (C1 to C8) alcohol, or
a combination of lower aliphatic alcohols; and/or
[0081] the alcohol may be ethanol; and/or
[0082] the alcohol may be in an aqueous solution comprising from
about 85 v/v % to about 100 v/v % of alcohol; and/or
[0083] the aqueous solution may have a volume sufficient to
submerge the tissue; and/or
[0084] the alcohol may be an aqueous solution comprising 95 v/v %
of alcohol; and/or
[0085] the step of treating the fixed tissue with an alcohol may be
performed for about 12 hours to about 48 hours; and/or
[0086] the step of treating the fixed tissue with an alcohol may be
performed for at least 24 hours; and/or
[0087] the step of treating the fixed tissue with an alcohol may be
performed at a temperature between about 15.degree. C. and about
30.degree. C.; and/or
[0088] the polyol may be a lower aliphatic diol or triol (C1 to
C4), or a combination of lower aliphatic diols or triols;
and/or
[0089] the polyol may be glycerol; and/or
[0090] the polyol may be in water or in a 0.9 wt % aqueous saline
solution comprising from about 20 v/v % to about 100 v/v % of
polyol; and/or
[0091] the polyol may be in a 0.9 wt % aqueous saline solution to
produce a polyol/saline solution comprising about 50 v/v % of
polyol; and/or
[0092] the polyol/saline solution may have a volume sufficient to
submerge the tissue; and/or
[0093] the step of treating the alcohol-treated fixed tissue with a
polyol may be performed for about 12 hours to about 48 hours;
and/or
[0094] the step of treating the alcohol-treated fixed tissue with a
polyol may be performed for at least 24 hours; and/or
[0095] the step of treating the alcohol-treated fixed tissue with a
polyol may be performed at a temperature between about 15.degree.
C. and about 30.degree. C.; and/or
[0096] the tissue may be in the form of a tissue component, a valve
assembly for a bioprosthetic valve or a fully assembled
bioprosthetic valve incorporating the tissue; and/or
[0097] the tissue component may be a tissue patch for use in
cardiac repairs; and/or
[0098] the prosthetic valve may be a prosthetic heart valve;
and/or
[0099] the prosthetic heart valve may be a surgical heart valve;
and/or
[0100] the prosthetic heart valve may be a collapsible
transcatheter heart valve.
[0101] The present application also discloses tissue prepared by
the described methods, and a valve assembly for a bioprosthetic
valve or a fully assembled bioprosthetic valve incorporating the
tissue.
[0102] Although the disclosure herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present disclosure. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
disclosure as defined by the appended claims.
* * * * *